Lessons from history
"In tests, we were able to draw an indicated vacuum of 27.5 inches – equivalent to a pressure of 60mmHg, or an altitude of 60,000ft (18,290m)."
"With the pump fired up and connected to the REHAB chamber, we managed to draw a vacuum of 20mbar – equivalent to around 76,500ft, or 23,300m - pretty well spot on our target of 15mmHg."
Aaaagh! One minute it's vacuum in "inches", then it's pressure in "mmHg" then it's pressure in mbar. Several times the units appear compared on against the other in the same sentence!
It's a recipe for disaster. Please just work in one set of units to give the project a chance of working? People with bigger pockets than yours (like NASA) have trashed billions of dollars of equipment due to conversion errors. Learn from history.
Looks like the gauge on the latest equipment you've been given works in mbar. Get all the gauges working in mbar, and cross-calibrate them. Think of your goal target-pressures in mbar, and please never mention "inches" or "mmHg" ever again. Give LOHAN a chance to work at least.